Is there evidence for dimension-two corrections in QCD two-point functions?

The ALEPH data on the (non-strange) vector and axial-vector spectral functions, extracted from tau-lepton decays, are used in order to search for evidence for a dimension-two contribution $C_{2V,A}$ to the operator product expansion (other than $d=2\mathrm{}$ quark mass terms). This is done by means of a dimension-two finite energy sum rule, which relates QCD to the experimental hadronic information. The average $C_2\equiv {(C}_{2V}{+C}_{2A})/2\mathrm{}$ is remarkably stable against variations in the continuum threshold, but depends rather strongly on ${\Lambda }_{\mathrm{QCD}}.$ Given the current wide spread in the values of ${\Lambda }_{\mathrm{QCD}},$ as extracted from different experiments, we conservatively conclude from our analysis that $C_2$ is consistent with zero.